B&R Automation PC 3100 User Manual page 75

With long cable lengths, the voltage drop can result in greater potential differences between the bus devices, which
can hinder communication. This can be improved by running the ground wire with the others.
2.3.5.2.3.6 RS485 - Bus length and cable type
The maximum transfer rate of 115 kbit/s depends on the cable length and type of cable used.
Extension
1200 m
Preferably, the cable material used should have the following properties or deviate only slightly from them in order
to achieve an optimal transfer rate.
RS485 cables
Signal line
Cable cross section
Wire insulation
Conductor resistance
Stranding
Shield
Ground conductor
Cable cross section
Wire insulation
Wire cross section
Outer jacket
Material
Properties
Cable shield
2.3.5.2.3.7 Terminating resistor
A terminating resistor for the serial interface is already integrated in the IF option. A switch is used to switch the
terminating resistor on or off, but it is necessary to open the system unit for this purpose. A switched-on terminating
resistor is indicated by a yellow LED.
Automation PC 3100 User's manual V 1.00 Translation of the original documentation
Table 77: RS485 - Bus length and transfer rate
4x 0.25 mm² (24AWG/19), tinned copper stranded wire
1x 0.34 mm² (22AWG/19), tinned copper stranded wire
Table 78: RS485 cable requirements
Switch for
terminating resistor
LED for terminating resistor
Figure 11: 5AC901.I485-00 - Terminating resistor
Transfer rate
Typ. 115 kbit/s
Property
PE
≤82 Ω/km
Wires stranded in pairs
Pair shielding with aluminum foil
PE
≤59 Ω/km
PUR compound
Halogen-free
Composed of tinned copper wires
Technical data
75